In the fiber optics field the need frequently arises to transfer light from one fiber to another. One solution to this problem is the use of optical connectors. Optical connectors can have single or multiple fiber configurations. Single fiber connectors provide the connection of only one fiber to another single fiber. In multiple fiber connectors several fibers are simultaneously coupled with another set of similar fibers. The invention here disclosed applies to multiple fiber applications.
Because of their higher density, multiple fiber connectors are becoming very popular in fiber optic applications. The connection is performed by fixing the fibers inside channels contained in the ferrule. Two ferrules are coupled inside an adapter that has the function of aligning the fibers and keeping the connection together. When mated together a pair of connectors must have their respective contained optical fibers properly aligned in end to end fashion for efficient light transfer with the fiber in the other connector of the mated pair. One such type of connector is the MT (or “Mechanical Transfer”) type connector which is made in various numbers for up to 72 fibers (or “in a linear arrays”).
A connector having 72 channels would be arranged in 6 arrays of 12 fibers each. Any number of channels above 12 would be in multiples of 12, such as 12, 24, 36, 48, 60 and 72.
Prior art MT connectors includes a substantially rectilinear body having a front mating surface and a parallel rear surface. The protective buffer is removed from the ends of the fibers and the fibers enter the connector through the rear surface as part of a fiber ribbon cable. The holes by which the individual fibers are exposed at the front mating surface are formed with very precise tolerances. The fibers are set in place within the holes by epoxy or other suitable adhesives. The ends of the exposed fibers as well as the front mating surfaces are polished. Connector springs are often used to hold the mated pair of connectors together to ensure that the ends of the mating fibers remain in contact, under a standard mating force.
The required alignment is typically achieved in MT-type connectors by mounting two pins in the holes of one of the ferrules and each pin is held in place by a pin holder. After this assembly operation the ferrule becomes a male ferrule. By placing spacers (not shown) behind the corresponding holes on another ferrule, the second ferrule becomes a female ferrule. When male and female ferrules mate, the pins from the male ferrule penetrate into the holes of the female ferrules, and thus the desired alignment is achieved. This design is shown in Prior Art, FIG. 1. To introduce the pins, the holes typically should have a slightly larger diameter than the pins, thereby reducing the accuracy of the alignment and consequently the optical performance of the connection. Another disadvantage of the prior MT-type connector design is that the body of the ferrule has to be used as a datum during the polishing process necessary to terminate the optical fibers. This requires a higher degree of precision during manufacture of the ferrule body, typically molded from a plastic material. The new design of the present invention eliminates this requirement. Additionally, in the conventional MT-type connector the whole surface of the ferrule should be polished, including the area around the holes. The holes then need to be cleaned after polishing.
The object of the invention is to provide a simpler and more accurate MT-type ferrule. This is achieved by a gender neutral configuration. The guiding pins are placed in a recessed area of the body of the ferrule and are either over molded or immovably fixed in some other way to the ferrule body.
The guiding pins are over molded in the same mold as the fiber channels, which makes the positioning of these pins very accurate relative to the fiber channels. The length of the pins is such that they do not protrude beyond the contact surface and consequently the ferrules can be terminated with the pins attached. The pins can then be used as a datum for placement of the ferrules in the polishing machine, eliminating the need for tight tolerances with respect to the body of the ferrule. Additional accuracy can be achieved if the prior art method of transferring accuracy is used. In that method a fixture is used to align the fibers relative to each other in a fiber passageway and an adhesive is then applied to maintain the position of the fibers.
The fact that both ends of the connectors carrying the cables are identical facilitates their use by the installers. Only one type of gender neutral MT-type of connector need be kept in inventory. The smaller number of parts (there are no pin holders) also has inventory reduction advantages.
The alignment is achieved in this invention by a zero gap configuration between the alignment pins and the V-grooved adapter body. The pins are kept under pressure by a spring or spring clip to obtain zero gap positioning. In addition, the gap can be decreased by use of placing the pin in a precision sleeve or hole or better yet in a V-groove to eliminate the gap. As a result, the gap between conventional guide pins and guide holes of traditional MT-type connectors is eliminated, so as to provide for a more accurate connector.
Withdrawal and insertion forces are more consistent in the present invention than in conventional MT-type connectors since they are determined by the springs inside of the adapter and not by the always different gap between guide pins and guide holes. Because of the unavoidable tolerances in the guide pins and guide holes of every such pair, the elimination of the guide pins and guide holes of traditional MT-type connectors is a significant advantage. The area of the ferrule face surface that is polished together with the fibers is smaller in the design of the present invention. There is no plastic material to polish around the guide holes, since there are no such holes. The polishing process is thus faster, more consistent, more accurate, and can be more simply automated if necessary.
The cleaning operation after polishing is simpler and faster. In particular, there are also no pins to avoid when cleaning male ferrules and no hard to clean deep guide holes in female ferrules.
The mold for the new ferrules is cheaper since the outer body of the ferrule no longer needs tight tolerances because it will not be used as a datum during polishing. Accordingly, the outer body of the ferrule of the present invention does not need the same level of precision as a conventional MT-type connector.